ANDROID: fs: mpage: use bio op/op_flags instead of bio->bi_rw

Since commit eed25cd5 ("mpage: use bio op accessors"),
bio->rw argument is obsolete. Use bio op/op_flags instead.

Fixes: Change-Id: I26bd36f933108927d6903da04d8cb42fd9c3ef3d
       "ANDROID: fs: FS tracepoints to track IO."
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>